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Rules for keep left/keep right on dual carriageways

Post by iainhouse
Over the years, there has been quite a lot of discussion about the need for KL/KR instructions on limited-access dual carriageways. The informal guidelines (such as we have) are spread across several forum topics - in particular Keep right on motorways - decision?

In general, it seems that the majority of drivers do not like having KL/KR junctions unless they are really needed. They want to know the distance to their own exit, without having that "masked" by many "keep right" instructions. We also have to balance the need to give good instructions against the driver's responsibility to actually look through the windscreen and read the road signs.

I have come up with a more detailed set of guidelines for KL/KRs. We (the Country Admins) have discussed it and we would like to add this to the Wiki. I'm creating this topic for 2 reasons. The first is so that you can discuss it and ask questions as you wish. The second is so that we can discuss things like implementation issues or exceptions here. We can then add a link for this topic to the Wiki entry, without ending up with an enormously detailed Wiki entry covering every possibility. :lol:
Keep Left/Right Instructions on Dual Carriageways

The following is a set of guidelines for when and where to implement keep left/right instructions at exits from dual carriageways.
  • Definition: A lane drop is when one or more lanes of the main carriageway separate off onto a junction. Extra lanes which appear and for which you have to cross a dotted line to reach are not a lane drop
  • If there is no lane drop, you do not have a KL/KR
  • If there is 1 drop lane and 1 continuing lane, you have a KL/KR.
  • If there is 1 drop lane and 2+ continuing lanes, you have a KL/KR if you cannot easily rejoin the main carriageway, having accidentally left via the drop lane.
  • If there is 1 drop lane and 2+ continuing lanes, you have a KL/KR if the continuation of the main carriageway is a different road. Example: end of a Motorway continuing as an A road.
    Reasoning: drivers often would like an indication that the road is changing.
  • If there are 2+ drop lanes, you have a KL/KR
    Reasoning: if there are 2 drop lanes and you've accidentally kept to the left, correcting your mistake involves crossing another lane of possibly faster traffic.
The position of the KL/KR junction is also important. The general rule is to have the junction at the 0-mile gantry - in other words, when the distance to the junction on the signs counts down to zero. The problem is that drop lanes are often quite long. Whilst you should be in the correct lane at the 0-mile mark, most drivers change lane much later than that. It can also cause problems if there are any splits after the first one. You may get a second KL/KR instruction whilst it's still possible to change lanes from the first split. So:
  • Definition: The 0-mile point is the point at which the distance countdown on the signs reaches 0 - normally a gantry.
  • Definition: The separation point is the point at which the drop lane(s) is separated from the main carriageway by a solid white line.
  • The KL/KR split should normally be at the 0-mile point
  • If there is an instruction of any sort except roundabout within 1 km after the separation point, in either direction, then the KL/KR junction should be at the separation point instead of the 0-mile point
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Re: Rules for keep left/keep right on dual carriageways

Post by CTCNetwork
Hi,

Sterling work but:
The KL/KR split should normally be at the 0-mile point
My only concern is people do depend on their sat-nav rather too much despite there being a huge window infront of them!
The KL/KR - if given at the 0 mile may mean you have people trying to move over the hatching on the roads which also usually start at this point... No?

Des. . . ;)
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Re: Rules for keep left/keep right on dual carriageways

Post by DG567
This looks good to me.

I agree the 0-mile point is a potential source of confusion. I think some simplification would suit most editors best. I had to read and re-read the instructions, then look at some aerial/street photos and then re-read again.

I wonder if it's simpler to set the junction at the point where the lanes physically separate? Just like a turn instruction, I'd make sure I was on the left/right ready to turn at that point. There might be odd junctions where this wouldn't work but I don't think you'll cover every eventuality in the guidelines.

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Re: Rules for keep left/keep right on dual carriageways

Post by ditchi56
There's another issue which we should consider at the same time. Sometimes when we've wanted to persuade Waze to issue a "keep right" as well as a "keep left" (or "exit left"), we've found it necessary to create a short segment of a different name (normally no name). Normally, we've kept this segment very short, 5m being the normal.

Recently Waze has introduced "traffic jam bars", which, when you hit the back of a traffic jam, give you an estimate of how long it will take to get through the jam. This is supposed to be from the back of the jam to the front, irrespective of how many editor road segments the jam covers. However, it only works if the router recognises that the jam covers every segment, and it seems difficult for the router to recognise a jam on a very short segment.

So the short "keep right" hack segments are tending to split jams into two. People get a traffic bar with a jam time estimate, work through to (the short segment at) the end of it, and then 5m later find themselves in another jam with another time estimate. Or at least Waze, thinks it's a different jam, whereas of course it's all one to the user.

So it seems we need to stop using very short segments as part of our "keep right" hacks. I suspect we should make the minimum segment length around 100m, but that is purely a guess on my part.
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Re: Rules for keep left/keep right on dual carriageways

Post by ditchi56
Waze have now introduced an ability for editors to override the default instructions at junctions. This means that we can now have a "keep right" wherever we want one, without resorting to playing with road names or adding short segments. :mrgreen:

The best documentation I can find is here, although take with a small pinch of salt as it is written (in American :() for the road situations of the USA. However much of it is valid, in particular the recommendation to create a Map Comment (that's the other new thing that's just come in :)) whenever creating a turn instruction override.
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Re: Rules for keep left/keep right on dual carriageways

Post by ditchi56
"Continue ahead" is a strange one, it's in the TIO (Turn Instruction Override) drop-down list but disabled. Whether Waze originally had it in but decided it was a bad idea, or whether it will become available later, I've no idea.

Just to further confuse matters, everybody seems to talk about TIO's, but the drop-down list is headed "Voice Prompt". It's definitely not confined to voice though, it also affects the "next instruction" display on the app.

While I like the idea of creating a Map Comment to highlight every TIO, others don't. I understand the Americans are running a poll on it, which is heading for a "no". Not that we should necessarily follow their lead anyway.

One thing I think we can agree on, TIO's should not be routinely used on simple minor junctions where the correct instructions have traditionally been obtained by tweaking junction angles to reflect the road paint.

We're getting a bit away from the topic of this thread though. TIO's are definitely the way to go when we need a "keep right" on a dual carriageway. Goodbye to those short segments which disrupt detour avoidance and traffic jam bars :mrgreen: !

Happy New Year!
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Re: Rules for keep left/keep right on dual carriageways

Post by iainhouse
To start the discussion off, these are some questions Tim had.
Timbones wrote:what about when a single lane-drop splits into 2 lanes before the separation point?
I'd say that can be ignored. If it's a single lane drop at the point we place the junction, then it shouldn't matter if it later expands to 2. By that point the driver should be on the correct side of the obvious dotted line. If the drop starts as one but has become 2 by the point we place the junction on the map, then treat it as a 2 lane drop and have a KL/KR.
Timbones wrote:what about when the hard-shoulder turns into a lane-drop?
It can only be a lane drop if it's already a lane so, presumably, drivers would have been routed into it earlier. If we're considering a junction where there is normally a 1-lane drop but sometimes use of the hard shoulder may make it a 2-lane drop, then we treat the junction as a 2-lane drop. If it's normally an exit, but sometimes the hard shoulder is used and is a lane drop, then we treat it as a normal "exit" junction.
Timbones wrote:what about a lane-drop that is followed by a regular split that joins that first lane?
Generally with these "two routes to exit" junctions, don't we generally just map the first & ignore the second? If that's the case, then we keep doing that. If not, I think I'd like to look at an example.
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Re: Rules for keep left/keep right on dual carriageways

Post by iainhouse
The 0-mile point is where the countdown on the signs reaches zero. In other works "In 1 mile, get in the LH lane" says that you should do it in 1 mile. "In 1/2 mile..." means in half a mile...

So the 0-mile point is where the signs are telling you to be in the correct lane. You can be a good boy and do it earlier, but you don't have to. Normally, with a lane drop, this is where the lane markings change from the normal long dashes to very short, closely-spaced dashes. Good drivers are in the lane at this point. BMW drivers are normally in the wrong lane and doing 90mph and will wait to cross over until the solid white line is about to start.

The main point is not to contradict the road signs. If a sign says "in 1/2 a mile", but Waze says "in 1 mile", the driver might decide that this isn't his exit - instead there must be another one further up. He will then end up driving like a BMW driver - staying to the right until it's obvious he's about to miss his exit and then cutting in suddenly.

Unless there is a good reason not to match the signs (i.e. there is an instruction half way up the ramp that we must not have announced too early), we should always match the signs. Beyond that, we have to rely on people looking at the road signs and not just their phone.

This is also why I said "an instruction of any sort except roundabout". If the separation point hasn't been reached and Waze says "keep right" for a ramp split, the driver might move right back onto the main carriageway. If Waze says "at the roundabout" before the separation point, it's pretty obvious you are taking the exit.

I'm sure there will be some junctions where this scheme won't work. But if we can agree a set of rules that covers the vast majority, we can spend much less time worrying about each individual case.
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Re: Rules for keep left/keep right on dual carriageways

Post by iainhouse
The preference is really for matching the signs. If signs say the split is in 1 mile, but Waze is saying 1.5 or 2 miles, drivers may think there is another junction further up, not get over in good time, and then be suddenly changing lane at the point where they really shouldn't. That's using the 0-mile point and should cover the majority of situations.

The problem with always following that rule is when there are further splits (generally when the ramp splits again for 2 different directions) and that instruction is given too early. We have, in the past, tried some things to prevent that second instruction happening. For example, 2 overlapping segments so that the second instruction comes afterwards. Unfortunately, the only thing that will delay an instruction is another instruction and we can't have a random instruction given at a point where no instruction is needed. So that's when we need to move the first split to the separation point - and that should cover most of the junctions where the 0-mile point isn't appropriate.

These sorts of junctions vary widely. Whatever we decide, there will always be exceptions to the rules. All we can do is come up with the best set of rules we can to cover most situations. The more often you can follow the rules, the more mental resources you can save for other tasks.
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Re: Rules for keep left/keep right on dual carriageways

Post by iainhouse
There is a problem with the "continue straight" instruction so it has been temporarily removed. It WILL be coming.
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